Randomized trial shows that a new bimodal EMAT accurately detects defects in X80 steel pipes, indicating improved safety in pipeline inspections.
High-strength X80 steel is extensively used in modern long-distance oil and gas pipelines. Prolonged exposure to harsh environments leads to material loss, primarily through corrosion under insulation or at coating defects. This wall thinning compromises structural integrity and can lead to catastrophic failure. Conventional piezoelectric ultrasonic testing (UT) is widely employed for in-service pipeline inspection; however, its performance can be limited under high-temperature, rough or coated surface conditions, where maintaining consistent acoustic coupling with liquid couplants is challenging. In contrast, electromagnetic acoustic transducers (EMATs) enable non-contact operation and eliminate the need for surface preparation. However, most existing bulk-wave EMATs are limited to exciting a single ultrasonic wave mode, either longitudinal waves or transverse waves, which restricts their defect characterisation ability. To address this issue, a bimodal EMAT is developed that integrates a U-shaped permanent magnetiser with spatially distributed coils within a closed magnetic circuit. The design employs a common magnetic field with tailored components to concurrently generate and receive both longitudinal and transverse waves. A finite element model (FEM) is developed to assess the influence of defects in X80 steel plates on EMAT signals. Experimental results demonstrate that the bimodal EMAT can simultaneously excite and receive the two wave types, enabling accurate defect-depth quantification. By cross-validating the measurements derived from each wave mode, potential misinterpretations of defect presence or absence are effectively mitigated.
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Shi et al. (2026) studied this question.